Galvanometer



} June29,f1943. H. T. BOEKER G'ALVANOMETER Filed May 25, 1940 ZOFUU EmQ I00 200 300 sop 700800 900 I000 FREQUENCY Patented June 29, 1943 UNITED STATES PATENT OFFICE GALVANOMETER Harold T. Becker, Chicago, Ill., assignor to General EiectricX-Ray Corporation, Chicago, 111., a corporation of New York Application May 25, 1940, Serial No. 337,177

7 Claims.

My invention relates in general to electrical measurement, the invention pertaining more particularly to electro-magnetic galvanometer construction.

' An important object of the present invention is to provide an electro-magnetic galvanometer in which the action of the instrument is substan-' frequency response for all frequencies up to frequencies of the order of 1,000 cycles per second in order to indicate all of the harmonics contained in the heart action under-observation.

Another important object is to provide an instrument of the character mentioned of sumciently rugged construction to withstand the vibration and shocks to which portable indicating and recording apparatus is necessarily exposed in service. g

Another, important object is to provide an in tion;

description, which, taken in connection with the accompanying drawing, discloses a preferred embodiment of the invention.

Referring to the drawing:

Figure 1 is a graphical representation of galvanometer frequency response; I

Figure 2 is an enlarged sectional view through a galvanometer embodying my present inven- Figure 3 is an enlarged somewhat diagrammatic representation of the armature and mirror mount forming a part of the galvanometer shown in Figure 2; and

Figure 4 is a sectional view taken substantially along the line 4-4 in Figure 2.

To illustrate my invention, I have shown on v the drawing a galvanometer H, comprising an dicating device having a movable mirror mounting in which frictional resistance to movement is a minimum; a further object being to mount the mirror at one end of a thin spring steel rib-' bon, the other end of which is fastened to the armature-of the galvanometer, and to confine the ribbon between opposed coaxial needle supports,

v whereby to obtain substantially undamped move- ,adjustment and operation; to provide a galvanometer in which the. mechanical parts are substantially free of the damping effects of friction; to provide a galvanometer having a sub stantially fiatfrequency response; and, in general, to provide a galvanometer suitable for use,

in accurately recording electrical phenomena fluctuating within the audio frequency range, as, for example, the recordation of voice or music on soundtrackof motion picture film and the recordation of heart sounds or cardiac voltages.

These and numerous other important objects,

actuating coil l3 mounted in operative position with respect to a core l5, an armature H, and a movable mirror mounting I9 connected to the armature.

The core forms a magnetic circuit and comprises preferably a permanent magnet 2| provided with preferably silicon steel pole pieces 23 mounted on the poles of the magnet 2| in opposing relationship, the pole pieces being notched or cut out, as at 25, to provide aspace in'which the coil I3 is mounted, said pole pieces each comprising arms 21 and 28 on opposite sides of ,the notches 25, the corresponding arms of the pole pieces being disposed in facing. spaced apart relationship to provide spaces between the pole pieces at the opposite ends of the coil l3 in which spaces the armature I1 is mounted.

advantages, and inherent functions of the inventlon will be fully understood from the following The armature I! preferably comprises a silicon steel stem having an end 38 anchored in an armature support 29, which is fastened in any suitable fashion rigidly with respect to the core l5. The armature l1 comprises preferably a flat strip of material and extends from its mounting in the air gap between the facing arms 21 of the pole piece on one side of the coil, thence through the coil, which is wound preferably on a suitable spool 31 to give the armature ample clearance for movement within the coil. The end 35 of the armature I1 remote from the 'mounting 29 extends in the space between the facing ends of the arms 28 of the pole pieces.

When the coil I3 is energized, the end 35 of the armature I! will be caused to move under the combined influences of the magnet 21 and the magnetic effect produced by the energized 'coil l3. a The movement of the armature, transferred to'the movably mounted mirror l9, will cause the same to move in exact accordance with the movement of the armature, providing there is no frictional retardation ordamping or lost motion in the connection between the armature and the mirror. slight, may be amplified by arranging the mirror to reflect light from a fixed source 31 onto a recording surface 39 of any convenient character such, for example, as a light-sensitive film.

In order to eliminate lost motion and the effects of mechanical friction from the armaturemirror connection, the mechanism I9 comprises a ribbon 4| of suitable material, such as steel or phosphor bronze, to one end of which a mirror 43 is attached, the other end of the ribbon 4| being fastened, as by means of silver solder or spot welding, to the end 35 of the armature H. The ribbon 4| is fixed on the armature preferably in alignment therewith and extends between a pair of coaxial restraining needles 45, the points of which engage .the opposite sides of the ribbon 4| substantially on the medial axis thereof.

The needles, 45 are preferably supported in embossments 41' formed on the arms 28 of the pole pieces 23, the needles preferably being threaded in said embossments, whereby thesame may be axially adjusted therein and fastened in adjusted position as by the clamp nuts 49.

The coil l3 comprises a suitable number of turns of preferably Copper wire'wound upon the spool 3| which is fastened in place upon the pole pieces 23 in any suitable or convenient fashion. Suitable leads 50 arerof course, provided for connecting the coil with the external circuits in which exist the electrical phenomena to be indicated or recorded. I provide for electrically dampening the galvanometer by applying means forming a closed circuit around the coil. Said circuit forming means may take the form of an annular band 5| of suitable conducting material, such as copper, applied at the periphery of the coil l3, or may comprise several turns of con-- ductor wire applied to the coil.

In order to provide for adjusting the damping eifectof the circuit forming means 5|, the circuit mayinclude an adjustable resistor 53 inserted in series in the damping circuit, as by interrupting the band 5|, as at 55, and connecting the adjustable resistor 53 in the circuit at said interruption, as clearly shown in Figure 4 of the drawing. a

When current flows through the coil |3 in the direction indicated by the arrows in Figure 2, a

north pole is established at the end 35of the a in the armature divides, as'shown, with part Dfz of the total armature flux flowing through the air gap H and the south pole piece'23 of the permanent magnet, thence back to the armature Mirror movement, though cordance with the stated conditions.

. surface 39 by an amount exactly proportional to the current flowing in the coil l3 so long as through the air gap l8, while the balance DI: of the flux flows through the air gap l2 and the in the air gap I4 is cumulative withrespect to the flux ii, the steady flux through the air gaps caused by the action of the permanent magnet,

while in the air gap l2, the flux Dfa opposes or is difierential with respect to the steady flux ii. The forcmtending to pull the armature toward the south pole is therefore greater than that tending to pull the armature toward the north pole. These forces may be expressed mathematically as follows:

The resultant flux in the air gap I2 is .fi-Df3 and in the air gap 4 is f1+Dfa The force tending to pull the armature toward the north pole is while the force tending to pull the armature toward the south pole is The resultant force on the armature is therefore If the armature is not saturated, the total flux therein will be directly proportional to the current flowing in the coil 3 so that By substituting the foregoing value for 13/3 in the preceding equation because ii is constant. i

For very small deflections of the armature, the elastic limit of the steel is not exceeded, and therefore the deflection of the armature is proportional to the force or D=K4.Im.sin Wt., in which Im. sin Wt.

is current in the coil. I

The foregoing equation indicates that the deflection is proportional to the current in the coil, providing the galvanometer is designed in ac- Consequently, a light beam emanating from the source 3l'will be deflected by the mirror 43 upon the the deflection of the armature is slight and the elastic limit of the steel is not exceeded.

When a force is exerted-upon the armature due to the flow of current in the coil IS, the armature will be deflected, as indicated in Figure 3 of the drawing, to'a position shown in dotted lines. If T: be the angle between the original and deflected positions, then for very small deflections of the armature, the following geometric relations are substantially true:

where a equals the length of the armature l1 and b equals the distance along the ribbon 4| from the end of the armature to the restraining pins 45.

Since the mirror 43 is mounted rigidly on the end of the ribbon 41, it will be deflected through an angle T1; and from the foregoing equation, it can be seen that by making b relatively small compared with a, a large multiplying factor for the sensitivity of the instrument can be obtained.

The foregoing geometric relation holds true for small deflections of the armature .where movement of the armature'does not cause any appreciable bending of the ribbon 4 l.

Instruments embodying my present invention have a substantially fiat frequency response for gaging the opposite sides of said ribbon interall frequencies up to the order of 1000cycles per second, as shown in the curve B in Figure 1, in which curve A represents the typical response oi coil type instruments of the character hereto fore available. It will be noted that curve B includes a peak portion C, which represents a phenomenon caused by the action of the springs at resonance. The resonant eiIect, however, occurs at the upper limit of the frequency range of the instrument and will not aifect the operation of the sam within its normal working limits.

It is thought that the invention and numerous of its attendant advantages will be understood from the foregoing description, and it is obvious that numerous changes may be made in the form. construction and arrangement of the several parts without'departing from the spirit or scope invention, or sacrificing any of its attend,-

a preferred embodiment for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

mediate the ends thereof.

4. In an instrument of the character described,

including an armature having an end movable in response to electrical impulses, the combination with said armature of a mirror, a resilient ribbon of self-supporting material having an end rigidly fastened to the movable end of said armature, said mirror being rigidly fastened to the other end of said ribbon, and confining means comprising coaxial aligned pins in position engaging the opposite sides of said ribbon intermediate the ends thereof, said pins being adjustable in the direction of their aligned axes.

5. In an instrument of the character described,

Q an armature movable in response to electrical fant advantages, the form herein described being 1. In an instrument of the character described, j

including an armature movable in response to electrical impulses, the combination with said armature of means forming a flexible extension on said armature, a mirror on said extension, and means confining said extension for rocking movement about an axis extending substantially midway between the armature and the mirror.

2. In an instrument of the character described, including an armature movable in response to electrical impulses, the combination, with said armature, of means forming a flexible extension on said armature, a mirror on said extension, and means comprisingopposing abutments on opposite sides of said extension for confining said extension for rocking movement about an axis located between the armature and the mirror and spaced from said mirror.

3. In an instrumento'f the character described, including an armature having an end movable I in response to electrical impulses, the combination with said armature of a mirror, a resilient ribbon of self-supporting material having an end rigidly fastened to the movable end of said armature, said mirror being rigidly 'i'astened to impulses, said armature comprising a member rigidly anchored at one end whereby armature movement is confined by theelasticity of the armature material, means forming a flexible extension on said armature, a mirror on said extension, and means forming abutmentson opposite sides of said extension for confining said extension for rocking movement about an axis disposed between the armature and the mirror.

6. In an instrument of the character described, an armature movable in response to electrical impulses, said armature comprising a member rigidly anchored at one end whereby armature movement is confined bythe elasticity of the armature material, means forming a flexible extension on'said armature, a mirror onsaid extension, and-co-axial pins aligned in position engaging opposite sides of said flexible extension for confining the movement thereof between the armature and the mirror.

7. In an instrument of the character described, an armature movable in response to electrical impulses, said armature comprising a member rigidly anchored at one end whereby armature movement is confined by the elasticity of the armature material, a resilient ribbon of flexible self-supporting material having an end rigidly fastened to said armature to'i'orm a flexible extension on said armature. a mirror on said extension, and means confining said extension for tilting movement about an axis therein and spaced from said mirror. 1

HAROLD. '1'. 30mm 

